Objective: Newborns who suffer from jaundice and/or receive phototherapy (PT) are at a higher risk of developing asthma. In this study we aimed to investigate the relationship between bilirubin and peripheral eosinophil counts in newborns with severe hyperbilirubinemia needing PT. Methods: In this study, a retrospective analysis was performed on 306 newborns with severe hyperbilirubinemia with gestational age .35 weeks (Group 1) and the control group consisted of 295 age and gender-matched newborns (Group 2). Total serum bilirubin, hemoglobin, albumin, leucocyte and eosinophil counts before and after PT were recorded from medical charts. Findings: All the patients in Group 1 received phototherapy and 77 (25.2%) of them needed exchange transfusion (ET). Before receiving PT, the patients in Group 1 had lower levels of Hb and higher levels of total serum bilirubin and lymphocytes than those in Group 2 although there was no statistically significant difference with regard to peripheral eosinophil counts. Eosinophils were detected to be numerically lower in Group 1. Higher bilirubin subgroups had also lower eosinophil counts. The patients in Group 1 had lower levels of Hb, leucocyte, albumin and higher levels of eosinophil following PT. Conclusion: Peripheral eosinophil count may be affected by bilirubin levels and/or phototherapy. There is a need for further clinical research based on different models.